Field of Invention
The present invention relates to a field of universal coupling, and more particularly to a method for repairing break of a universal connecting rod of a universal coupling.
Description of Related Arts
At present, universal connecting nods of heavy load and over load linear universal couplings widely used in main driving devices of heavy machines such as hot tandem cogging mills, large merchant steel rolling mills, punch machines, as well as middle-width thick plate and Steckle mills are easy to be damaged: on the one hand, heavy load and over load universal couplings used in the above heavy machines are huge, rotary diameter thereof is 650 mm to 1300 mm, torque thereof is 2300 kn·m to 19405 kn·m, resulting in huge impact load at moments of starting or emergency power off, i.e. impact load with large instant torque; on the other hand, during working, the universal connecting nods will be affected by a force of a high frequency alternating impact load.
In summary, reason of the above break is: fatigue break at a root of an axle neck is a main failure mode of the universal connecting rod. Technical difficulties during solving a strength problem of the component are as follows: firstly, equipment space is a restricting factor, which means a load capacity of the heavy load and over load linear universal couplings cannot be improved by increasing a size of the universal connecting rod; secondly, the device has a problem of stress concentration during working, which will result in the fatigue break at the root of the axle neck of the universal connecting rod; finally, the conventional universal connecting rod is mainly formed by billet steel hot forging, then the axle neck thereof is processed with a CNC (computerized numerical control) machine. However, a transition structure of the root of the axle neck of the universal connecting rod is usually single circular arc surface smooth transition or step type transition. The universal connecting rod with single circular arc surface smooth transition is restricted by a size of a linear axle structure because of a transition arc size is too large, which cannot overcome the problem of stress concentration problem. Stress concentration still exists at the root of the axle neck of the universal connecting rod with such transition, so break is still easy to happen. In addition, machining of such structure is difficult, and manufacturability thereof is poor, which lowers production efficiency. Therefore, a step type transition fillet structure is mainly used. Stress concentration exists wherein sudden change of cross sections of the universal connecting rod happens, that is to say, under heavy load and torque is more than 2800 kn·m, break is extremely easy to happen, which cannot be effectively solved at present.
As a result, an axle end and an axle body of the universal connecting rod, a key component of the heavy load and over load universal coupling are easy to break, resulting in out of service. Metal materials, strength, temperature, technology, process and heat deformation of common welding crack repairing are difficult to control, resulting in that a welding temperature of a welding bead is too high, which causes heat deformation. In addition, because of improper welding techniques, welding stress resides at a welding part is too large and strength is not even, which generates new cracks, and intensifies heat stress deformation. Therefore, new deformation is inevitable, which will lead to unusable and directly affects normal production. That is a major problem that enterprises urgently need to solve.
Development of a repairing technique without heat stress deformation is a subject of universal shaft coupling repairing.
European patent EP1930116 A2 discloses a crack repairing method, which directly deposits a nano alloy 28 in the crack, then deposits a filler alloy 30 on the nano alloy 28. Preferably, the above alloys are nickel or cobalt base superalloy for steam turbine fittings. The above method cannot repair a potential crack.
U.S. patent US2005015980A1 discloses a method for repairing cracks of a steam turbine part, which drills a repairing groove 18 at a crack 16. A depth of the repairing groove 18 cannot be extended to a cavity 14 beneath, and the repairing groove 18 is drilled by manual grinding, machining or electrical discharge machining. A filler 20 is deposited in the repairing groove 18 by a. The micro plasma welding machine with low ampere inputs heat to the repairing groove 18 of the input heat, so as to form a thin heat impact layer 22 at a surface of the repairing groove 18 of the steam turbine part. The heat impact layer reduces strength of the steam turbine part repaired.